1. Field of the Invention
The present invention relates to an optical information recording medium onto/from which information is recorded/reproduced using, for example, light beams.
2. Description of the Related Art
From the past, disc-like optical information recording media generally typified by a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc; registered trademark) have been widely used as optical information recording media.
Meanwhile, in optical information recording/reproducing apparatuses that support the optical information recording media, various types of information including various contents such as music contents and video contents and various types of data for computers are recorded onto the optical information recording media. Particularly in recent years, an information amount is increasing due to high-definition videos and high-quality-sound music, and there is a demand to increase the number of contents that can be recorded onto a single optical information recording medium. Thus, capacities of the optical information recording media are required to be additionally increased.
In this regard, as a technique of increasing a capacity of an optical information recording medium, there is proposed an optical information recording medium in which a plurality of minute holograms as recording marks formed by interferences of two types of light beams are formed in a thickness direction of the optical information recording medium so as to overlap one another. In this optical information recording medium, information corresponding to a plurality of layers are recorded within a single recording layer (see, for example, Japanese Patent Application Laid-open No. 2008-71433; hereinafter, referred to as Patent Document 1).
The optical information recording medium disclosed in Patent Document 1 has a disadvantage that an optical system thereof becomes complex since it needs two types of light beams. On the other hand, as the optical information recording medium, there is also proposed an optical information recording medium onto which, by heat generated by irradiation of one type of light beams, cavities (bubbles) are formed in the vicinity of a focal point of the light beams and information corresponding to a plurality of layers is recorded within a single recording layer by using the cavities as recording marks (see, for example, Japanese Patent Application Laid-open No. 2005-37658; hereinafter, referred to as Patent Document 2).